Embryologic Correlations

CASE 6: Limb-Body Wall Complex

Clinical History:

A 31-year-old G4 P2 Ab1 woman has a serum triple screen at 19 weeks gestation. The alpha fetoprotein (AFP) is 6 multiples of the median (MoM), with low human chorionic gonadotropin (HGG) and normal unconjugated estriol (uE3). An ultrasound reveals an anterior abdominal wall defect with herniation of the abdominal contents. The right hand is not visualized. There is a large deep asymmetric left cleft lip and palate without a well-defined nose. The pregnancy is terminated.

Examination of the male fetus in surgical pathology shows a large abdominal wall open defect. There is severe scoliosis. A fibrous band extends from the right edge of this defect to the right arm, constricting the forearm, with absence of the right hand. A fibrous band extends from the upper edge of the abdominal defect across the head, cutting a deep cleft through the mouth and nose. A tortuous 3 vessel umbilical cord extends from the right edge of the abdominal wall defect to the placenta and is only 10 cm long.

What problem in embryogenesis lead to these findings?

This is early amnion disruption. The developing fetal ventral body wall does not develop normally. There can be formation of fibrous adhesions. Disruptions are asymmetric and variable. Torso, extremities, and/or head can be affected.

Name the abdominal wall defect.

This is gastroschisis, which is a ventral abdominal defect uncovered by skin or membranes and located to the right or left of midline. The umbilical cord is at the defect's margin.

What is scoliosis?

Curvature of the spine.

What would a karyotype show?

46, XY.

What is the name for this abnormality?

Limb-body wall complex. Since about 40% of cases are accompanied by fibrous bands (amniomic bands), the term amnionic band syndrome is sometimes applied.

In some cases, a skull defect is present, but cerebral tissue is seen. What is the name for this?

Exencephaly. This is the rarest form of neural tube defect. It is a disruption, not a malformation inherent to the neuraxis.

What chromosomal abnormalities will lead to abnormalities in the triple screen?

Down syndrome (trisomy 21) results in a low AFP, low uE3, and high HCG.